Method and apparatus of transmitting ack/nack

ABSTRACT

A method for transmitting an uplink signal by a user equipment (UE) in a wireless communication system. The method according to one embodiment includes receiving, by the UE, a physical downlink control channel (PDCCH) via one or more resource units; receiving, by the UE, a physical downlink shared channel (PDSCH) indicated by the received PDCCH; and transmitting, by the UE, a physical uplink control channel (PUCCH) using a PUCCH resource in response to the received PDSCH. An index of the PUCCH resource is determined by adding a first index offset and a second index offset to a lowest index of the one or more resource units. The first index offset is signaled via the PDCCH and the second index offset is signaled via higher layer signaling.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/147,812 filed on Aug. 4, 2011, which is the national phaseof PCT International Application No. PCT/KR2010/001814 filed on Mar. 24,2010, which claims the benefit of U.S. Provisional Application No.61/163,442 filed on Mar. 25, 2009, and Korean patent application No.10-2010-0021097 filed on Mar. 10, 2010. The entire contents of all ofthe above applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system. And,more particularly, the present invention relates to a method andapparatus of transmitting ACK/NACK.

2. Discussion of the Related Art

A wireless communication system has been widely developed to providevarious kinds of communication services such as voice and data.Generally, the wireless communication system is a multiple access systemthat can support communication with multiple users by sharing availablesystem resources (bandwidth, transmission power, etc.). Examples of themultiple access system include a code division multiple access (CDMA)system, a frequency division multiple access (FDMA) system, a timedivision multiple access (TDMA) system, an orthogonal frequency divisionmultiple access (OFDMA) system, a single carrier frequency divisionmultiple access (SC-FDMA) system, and a multi carrier-frequency divisionmultiple access (MC-FDMA) system.

If a wireless communication system transmits a data unit (e.g., packet),a receiver should notify the success or failure of the data unitreception to a transmitter. If the data unit reception is successful, anACK (acknowledgement) is transmitted, so that the transmitter cantransmit a new data unit, and if the data unit reception is unsuccessful(or failed), a NACK (Negative-ACK) is transmitted, so that thetransmitter retransmits the corresponding data unit. Such operation isreferred to as an ARQ (Automatic Repeat reQuest). An HARQ (hybrid ARQ)is a method consisting of a combination of the ARQ and channel coding.The HARQ may combine a retransmitted data unit with an already-receiveddata unit, thereby reducing an error rate. In the HARQ, the ACK/NACK(A/N) is transmitted by using a physical channel signaling method. Themethod for realizing the HARQ may broadly include a Chase Combining (CC)method and an Incremental Redundancy (IR) method.

SUMMARY OF THE INVENTION

The present invention is devised to provide a method and apparatus oftransmitting ACK/NACK (Acknowledgement/Negative-ACK) signals in awireless communication system. More specifically, the present inventionrelates to a method and apparatus of efficiently assigning resources fortransmitting ACK/NACK signals in a wireless communication system. Thetechnical objectives that are to be realized by the present inventionwill not be limited only to the technical objects pointed out herein.Other technical objectives that have not yet been mentioned herein willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention.

In an aspect of the present invention, provided herein is a method oftransmitting an ACK/NACK (Acknowledgement/Negative-ACK) signal at a userequipment in a wireless communication system, the method including:receiving a first downlink control channel from a base station;receiving scheduling information through a second downlink controlchannel from the base station; deciding an uplink resource index fortransmitting an ACK/NACK signal associated with the scheduling byconsidering the first control channel when the first control channel hasa predetermined format; and transmitting the ACK/NACK signal to the basestation by using an uplink resource indicated by the uplink resourceindex.

In another aspect of the present invention, provided herein is a userequipment including an RF (Radio Frequency) unit configured to transmitand receive wireless (or radio) signals to and from a base station; amemory for storing information transmitted and received to and from thebase station and parameters required for operations of the userequipment; and a processor being connected to the RF unit and the memoryand being configured to control the RF unit and the memory, wherein theprocessor is configured to perform receiving a first downlink controlchannel from a base station; receiving scheduling information through asecond downlink control channel from the base station; deciding anuplink resource index for transmitting an ACK/NACK signal associatedwith the scheduling by considering the first control channel when thefirst control channel has a predetermined format; and transmitting theACK/NACK signal to the base station by using an uplink resourceindicated by the uplink resource index.

Whether or not the first downlink control channel has the predeterminedformat may be determined based upon a structure of the first downlinkcontrol channel (e.g., length of DCI (Downlink Control Information)).Also, whether or not the first downlink control channel has apredetermined format may be determined based upon information carried bythe first downlink control channel (e.g., contents of DCI (DownlinkControl Information)). In this case, when the first downlink controlchannel has a predetermined format, the first downlink control channelmay carry a null (e.g., predefined ‘0’s or ‘1’s) value. Furthermore,whether or not the first downlink control channel has a predeterminedformat may be determined based upon a masking code or scrambling codeapplied to the first downlink control channel. Finally, when the firstdownlink control channel has a predetermined format, the first downlinkcontrol channel may be configured of 1 CCE (Control Channel Element).

In another aspect of the present invention, provided herein is a methodof transmitting an ACK/NACK (Acknowledgement/Negative-ACK) signal at auser equipment in a wireless communication system, the method including:receiving scheduling information from a base station through a downlinkcontrol channel; receiving a data unit from the base station through adownlink shared channel based upon the scheduling information; decidingan uplink resource index for transmitting an ACK/NACK signal withrespect to the data unit by using a resource index configuring thedownlink control channel and by using index modification informationassociated with the downlink control channel; and transmitting theACK/NACK signal to the base station by using an uplink resourceindicated by the uplink resource index.

In a further aspect of the present invention, provided herein is a userequipment including an RF (Radio Frequency) unit configured to transmitand receive wireless (or radio) signals to and from a base station; amemory for storing information transmitted and received to and from thebase station and parameters required for operations of the userequipment; and a processor being connected to the RF unit and the memoryand being configured to control the RF unit and the memory, wherein theprocessor is configured to perform receiving scheduling information froma base station through a downlink control channel; receiving a data unitfrom the base station through a downlink shared channel based upon thescheduling information; deciding an uplink resource index fortransmitting an ACK/NACK signal with respect to the data unit by using aresource index configuring the downlink control channel and by usingindex modification information associated with the downlink controlchannel; and transmitting the ACK/NACK signal to the base station byusing an uplink resource indicated by the uplink resource index.

The downlink control channel may include a PDCCH (Physical DownlinkControl Channel), and the uplink resources may include a PUCCH (PhysicalUplink Control Channel) resource. Also, the resource index used fordeciding the uplink resource may include a first index among resourceindexes configuring the downlink control channel.

The index modification information may include an (absolute/relative)offset value. And, the index modification information may be included ina DCI (Downlink Control Information) of the downlink control channel.Additionally, the index modification information may be verified byusing a masking code or scrambling code applied to the downlink controlchannel. Furthermore, the index modification information may beidentified by using information of a subframe through which the downlinkcontrol channel is received or by using information of a componentcarrier.

The downlink control channel may be received through a downlink subframethat is not paired with an uplink subframe in which the ACK/NACK signalis transmitted. And, the downlink control channel may be receivedthrough a downlink subframe that is paired with an uplink subframe forbackhaul communication.

According to the embodiments of the present invention, in a wirelesscommunication system, the ACK/NACK signals may be efficientlytransmitted. More specifically, in a wireless communication system,resources for transmitting the ACK/NACK signals may be efficientlyassigned (or allocated).

The effects that can be achieved in the present invention will not belimited only to the effects pointed out in the description of thepresent invention. Other effects that have not yet been mentioned hereinwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andalong with the description serve to explain the spirit and scope (orprinciple) of the invention.

FIG. 1 illustrates a network structure of an E-UMTS (Evolved UniversalMobile Telecommunications System).

FIG. 2 illustrates an exemplary wireless frame structure used in an LTE.

FIG. 3 illustrates an exemplary downlink subframe structure used in anLTE.

FIG. 4 illustrates an exemplary uplink subframe structure used in anLTE.

FIG. 5 illustrates an exemplary uplink control channel structure used inan LTE.

FIG. 6 illustrates an exemplary correspondence between a PUCCH and aPDCCH for transmitting ACK/NACK.

FIG. 7 illustrates an exemplary correspondence between a PUCCH and aPDCCH for transmitting ACK/NACK.

FIG. 8 and FIG. 9 illustrate examples of a user equipment transmittingACK/NACK, when a non-paired subframe exists.

FIG. 10 illustrates an example of performing communication under amultiple component carrier condition.

FIG. 11 illustrates an example of assigning (or allocating) resourcesfor transmitting ACK/N ACK signals according to an embodiment of thepresent invention.

FIG. 12 illustrates an example of assigning (or allocating) resourcesfor transmitting ACK/NACK signals according to another embodiment of thepresent invention.

FIG. 13 and FIG. 14 respective illustrate examples of assigning (orallocating) resources for transmitting ACK/NACK signals according to yetanother embodiment of the present invention.

FIG. 15 illustrates an example of assigning (or allocating) resourcesfor transmitting ACK/NACK signals according to yet another embodiment ofthe present invention.

FIG. 16 illustrates an exemplary base station and an exemplary userequipment (or user terminal) that can be applied to the embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, structures, operations, and other features of the presentinvention will be understood readily by the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The embodiments of the present invention can be used forvarious wireless access technologies such as CDMA, FDMA, TDMA, OFDMA,SC-FDMA, and MC-FDMA. The CDMA can be implemented by wireless technologysuch as universal terrestrial radio access (UTRA) or CDMA2000. The TDMAcan be implemented by wireless technology such as global system formobile communications (GSM)/general packet radio service (GPRS)/enhanceddata rates for GSM evolution (EDGE). OFDMA can be implemented bywireless technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, and evolved UTRA (E-UTRA). The UTRA is a part of auniversal mobile telecommunications system (UMTS). A 3^(rd) generationpartnership project long term evolution (3GPP LTE) communication systemis a part of an evolved UMTS (E-UMTS) that uses E-UTRA. LTE-advanced(LTE-A) is an evolved version of the 3GPP LTE.

The following embodiments will be described based on that technicalfeatures of the present invention are applied to the 3GPP system.However, it is to be understood that the 3GPP system is only exemplaryand the present invention is not limited to the 3GPP system.

FIG. 1 is a diagram illustrating a network structure of an EvolvedUniversal Mobile Telecommunications System (E-UMTS). The E-UMTS may bereferred to as a Long Term Evolution (LTE) system. For details of thetechnical specifications of the UMTS and E-UMTS, refer to Release 7 andRelease 8 of “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE) 120, basestations (eNode B and eNB) 110 a and 110 b, and an Access Gateway (AG)which is located at an end of a network (E-UTRAN) and connected to anexternal network. Generally, the base stations can simultaneouslytransmit multiple data streams for a broadcast service, a multicastservice and/or a unicast service. One or more cells may exist for onebase station. One cell is set to one of bandwidths of 1.25, 2.5, 5, 10,and 20 Mhz. Different cells may be set to provide different bandwidths.Also, one base station controls data transmission and reception for aplurality of user equipments. The base station transmits downlink (DL)scheduling information of downlink data to a corresponding userequipment to notify the corresponding user equipment of time andfrequency domains to which data will be transmitted and informationrelated to encoding, data size, hybrid automatic repeat and request(HARQ). Also, the base station transmits uplink (UL) schedulinginformation of uplink data to the corresponding user equipment to notifythe corresponding user equipment of time and frequency domains that canbe used by the corresponding user equipment, and information related toencoding, data size, HIARQ. A Core Network (CN) may include the AG and anetwork node for user registration of the UE. The AG manages mobility ofa UE on a Tracking Area (TA) basis, wherein one TA includes a pluralityof cells.

FIG. 2 is a diagram illustrating a structure of a radio frame used inthe LTE system. Referring to FIG. 2, the radio frame has a length of 10ms(327200*T_(s)) and includes 10 subframes of an equal size. Each subframe has a length of 1 ms and includes two slots. Each slot has alength of 0.5 ms(15360*T_(s)). In this case, T_(s) represents a samplingtime, and is expressed by T_(s)=1/(15 kHz*2048)=3.2552*10⁻⁸ (about 33ns). The slot includes a plurality of OFDMA (or SC-FDMA) symbols in atime domain, and includes a plurality of resource blocks (RBs) in afrequency domain. In the LTE system, one resource block includes twelve(12) subcarriers*seven (or six) OFDMA (or SC-FDMA) symbols. Atransmission time interval (TTI) which is a transmission unit time ofdata can be determined in a unit of one or more subframes. Theaforementioned structure of the radio frame is only exemplary, andvarious modifications can be made in the number of subframes included inthe radio frame or the number of slots included in the subframe, or thenumber of OFDMA (or SC-FDMA) symbols included in the slot. FIG. 3illustrates an exemplary downlink subframe structure used in an LTE.Referring to FIG. 3, a downlink wireless frame includes 10 subframeseach having the same length. In a 3GPP ITE system, a subframe is definedas a basic time unit for packet scheduling with respect to an overalldownlink frequency. Each subframe is divided into schedulinginformation, and a time section for transmitting other controlinformation (control region) and a time section for transmittingdownlink data (data region). The control region starts from a first OFDMsymbol of a subframe and includes at least one or more OFDM symbols. Thesize of the control region may be independently set-up (or determined)for each subframe. The control region is used for transmitting L1/L2(layer 1/layer 2) control signals. The data region is used fortransmitting downlink traffic. Control channels being assigned to thecontrol region include PCFICH (Physical Control Format IndicatorCHannel), PHICH (Physical Hybrid-ARQ Indicator CHannel) and PDCCH(Physical Downlink Control CHannel).

The PDCCH corresponds to a physical downlink control channel, which isassigned to the first n number of OFDM symbols of a subframe. Herein, nis an integer more than or equal to 1, which is indicated by PCFICH. ThePDCCH is configured of one or more CCEs. Each CCE includes 9 REGs, andeach REG consists of 4 resource elements adjacent to one another whileexcluding a reference signal. A resource element corresponds to aminimum resource unit defined as 1 subcarrier×1 symbol. The PDCCHnotifies information on resource assignment (or allocation) oftransmitting channels PCH (Paging channel) and DL-SCH (Downlink-sharedchannel), Uplink Scheduling Grant, HARQ information, and so on to eachuser equipment (or user terminal) or user equipment group. The PCH(Paging channel) and the DL-SCH (Downlink-shared channel) aretransmitted through the PDSCH. Information on which user equipment (oneor a plurality of user equipments) data of the PDSCH are to betransmitted, and information on how the user equipments are to receiveand decode the PDSCH data are included in the PDCCH, thereby beingtransmitted. For example, it is assumed that a specific PDCCH isprocessed with CRC masking with an RNTI (Radio Network TemporaryIdentity) “A” and that information on the data being transmitted isbeing transmitted through a specific subframe by using a radio (orwireless) resource (e.g., frequency position) “B” and a transmissionformation information (e.g., transmission block size, modulation method,coding information, and so on) “C”. A user equipment of thecorresponding cell uses its own RNTI information to monitor the PDCCH,and a user equipment having the RNTI “A” receives the PDCCH. Then, byusing the information on the received PDCCH, the PDSCH indicated by “B”and “C” is received.

FIG. 4 is a diagram illustrating a structure of an uplink subframe usedin an LTE system. Referring to FIG. 4, the uplink subframe includes aplurality of slots (for example, two slots). The slot can include adifferent number of SC-FDMA symbols depending on a CP length. Forexample, in case of a normal CP, the slot includes seven SC-FDMAsymbols. The uplink subframe is divided into a data region and a controlregion. The data region includes a physical uplink shared channel(PUSCH), and is used to transmit a data signal such as voice. Thecontrol region includes a physical uplink control channel (PUCCH), andis used to transmit control information. The PUCCH includes a pair ofresource blocks (RBs) (for example, m=0, 1, 2, 3) located at both endsof the data region on the frequency axis, and is hopped using the slotas a boundary. The control information includes HARQ ACK/NACK, channelquality indicator (CQI), precoding matrix index (PMI), and rank index(RI).

FIG. 5 is a diagram illustrating a structure of a physical uplinkcontrol channel (PUCCH) for transmitting ACK/NACK.

Referring to FIG. 5, in case of a normal cyclic prefix (CP), a referencesignal (UL RS) is carried in three continuous symbols located in thecenter of the slot, and control information (i.e., ACK/NACK signals) iscarried in the other four symbols. In case of an extended CP, the slotincludes six symbols, wherein a reference signal is carried in the thirdand fourth symbols. ACK/NACK signals from a plurality of user equipmentsare multiplexed with one PUCCH resource by using a CDM mode. The CDMmode is implemented using cyclic shift (CS) of frequency spreadingand/or (quasi) orthogonal spreading codes for time spreading. Forexample, ACK/NACK are identified using different cyclic shifts (CS) ofcomputer generated constant amplitude zero auto correlation (CG-CAZAC)sequence (frequency spreading) and/or different walsh/DFT orthogonalcodes (time spreading). w0, w1, w2, w3 multiplied after IFFT obtain thesame result even though they are multiplied before IFFT. In the LTEsystem, PUCCH resources for transmitting ACK/NACK are expressed bycombination of frequency-time resources (for example, resource block),cyclic shift of sequences for frequency spreading, and (quasi)orthogonalcodes for time spreading. Each PUCCH resource is indicated using a PUCCH(resource) index.

FIG. 6 is a diagram illustrating an example of determining PUCCHresources for ACK/NACK. In the LTE system, PUCCH resources for ACK/NACKare not previously allocated to each user equipment but shared by aplurality of user equipments within a cell per timing point. In moredetail, the PUCCH resources used for ACK/NACK transmission correspond toPDCCH carrying scheduling information of corresponding downlink data. Ineach downlink subframe, an entire region where PDCCH(s) is transmittedincludes a plurality of control channel elements (CCEs), and the PDCCHtransmitted to the user equipment includes one or more CCEs. The userequipment transmits ACK/NACK through a PUCCH resource corresponding to aspecific CCE (for example, first CCE) among CCEs constituting PDCCHreceived therein.

Referring to FIG. 6, each square block in a downlink (DL CC) representsa CCE, and each square block in an uplink (UL CC) represents a PUCCHresource. Each PUCCH index corresponds to a PUCCH resource for ACK/NACK.It is assumed that information regarding PDSCH information istransferred through a PDCCH that includes CCEs Nos. 4 to 6 asillustrated in FIG. 6. In this case, the user equipment transmitsACK/NACK through PUCCH No. 4 corresponding to CCE No. 4 which is thefirst CCE of the PDCCH. FIG. 6 illustrates that maximum M number ofPUCCHs exist in the UL CC when maximum N number of CCEs exist in the DLCC. Although N may be equal to M (N=M), M may be different from N, andmapping between CCEs and PUCCHs may be overlapped.

In more detail, in the LTE system, PUCCH resource index is defined asfollows.

n ⁽¹⁾ _(PUCCH) =n _(CCE) +N ⁽¹⁾ _(PUCCH)  [Equation 1]

In this case, n⁽¹⁾ _(PUCCH) represents a PUCCH resource index fortransmitting ACK/NACK, N⁽¹⁾ _(PUCCH) represents a signaling valuetransferred from an upper layer, and n_(CCE) represents the smallestvalue of CCE indexes used for PDCCH transmission.

As shown in the equation 1, the PUCCH index for ACK/NACK transmission isdecided according to the first CCE used for PDCCH transmission. Andthen, the RB (Resource Block) index, orthogonal cover index, and cyclicshift value of the PUCCH resource for the actual PUCCH transmission aredecided according to the PUCCH index. eNB should reserve PUCCH resourcesthat are equal to the number of CCEs for PDCCH transmission. In casethat the number of CCEs for PDCCH transmission is more than 1, theremaining PUCCH indices which are mapped to remaining CCE indices exceptfor the first CCE are not used for actual PUCCH transmission. As shownin Equation 1, the PUCCH index used for transmitting ACK/NACK is decidedin accordance with a first CCE for PDCCH transmission. Thereafter, an RB(Resource Block) index for PUCCH transmission, an orthogonal coverindex, and a cyclic shift value are decided by using the PUCCH index.Since the base station should reserve a number of PUCCH resourcescorresponding to the number of CCEs used in the PDCCH transmission, whentwo or more CCEs are used in the PDCCH transmission, with the exceptionof the first CCE, the PUCCH index mapped to the remaining PUCCH is notused for the PUCCH transmission. FIG. 7 to FIG. 9 illustrate examples oftransmitting ACK/NACK. Generally, in an FDD (Frequency Division Duplex)system, the number of downlink subframes may be equal to the number ofuplink subframes, and each number may correspond to one another. Forexample, in case of the LTE system, each downlink subframe has a paireduplink subframe in association with at least the PUCCH transmission forACK/NACK signals. However, in case of the LTE-A system, a downlinksubframe that does not have a paired uplink subframe in association withthe PUCCH transmission may be generated in the FDD system and a TDD(Time Division Duplex) system.

For simplicity, in the present invention, a downlink subframe pairedwith an uplink subframe will be referred to as a paired subframe or anormal subframe. Also, a downlink subframe that is not paired with anuplink subframe will be referred to as a non-paired subframe or anextended subframe. A non-paired subframe may be generated for a varietyof reasons. For example, a non-paired subframe may be generated when itsrespective uplink subframe, in the FDD or TDD mode, is used for anotherpurpose (e.g., a backhaul link for a relay station). Also, a non-pairedsubframe may be generated when multiple downlink subframes in the TDDmode is linked to a single uplink subframe in association with theACK/NACK signal transmission. In this case, one of the multiple downlinksubframes may be assumed to be a paired subframe, and the remainingdownlink subframes may be assumed to be non-paired subframes.

In case the user equipment receives multiple PDSCHs within multipledownlink subframes (i.e., a paired subframe and non-paired subframes),the assignment of multiple PUCCH resources should be taken intoconsideration in order to transmit multiple ACK/NACK through a singleuplink subframe. For example, in case the user equipment receives 2PDSCHs (and PDCCHs delivering (or carrying) scheduling information onthe PDSCHs), it is assumed that one PDSCH exists in a non-pairedsubframe and that another PDSCH exists in a paired subframe. In thiscase, the user equipment shall ACK/NACK signals for its 2 respectivePDSCHs through a single uplink subframe.

Referring to FIG. 7, since DL subframe 1 has a paired uplink subframe(UL subframe 1), DL subframe 0 is a non-paired subframe, and DL subframe1 is a paired subframe. In the description of the present invention, thesubframe index ‘n’ is used for referring to the paired UL/DL subframes.And, it should be noted that the subframe index ‘n’ is not used forindicating the subframe number in the time domain. As shown in FIG. 7,the 2 PDSCHs are respectively received through 2 downlink subframes.User equipment A (UE A) generates an ACK/NACK for a respective PDSCHwithin each downlink subframe. Then, 2 ACK/NACK signals for 2 downlinksubframes should be transmitted through a single uplink subframe. Inthis case, user equipment A (UE A) should decide a PUCCH resource indexfor transmitting ACK/NACK signals. Meanwhile, if the same method ofassigning (or allocating) a PUCCH resource (e.g., using the first CCEused in the PDCCH transmission) is applied, a collision may occur in thePUCCH resources for transmitting ACK/NACK. Therefore, a method ofefficiently assigning (or allocating) PUCCH resources with respect tothe paired subframe and the non-paired subframe should be defined.

For this, the PDSCH (and the PDCCH delivering (or carrying) schedulinginformation on the PDSCH) for UE A may be transmitted only to the pairedsubframe or the non-paired subframe (FIG. 8). However, even if UE A isset to receive the PDCCH for the PDSCH only in the non-paired subframe,another user equipment (UE B) may receive the PDCCH for the PDSCHthrough the paired subframe. In this case, if the first CCE of the PDCCHfor UE A is identical to the first CCE of the PDCCH for UE B, theACK/NACK signal for UE A may collide with the ACK/NACK signal for UE B(FIG. 9).

FIG. 10 illustrates an example of performing communication under amultiple Component Carrier (CC) condition. The conditions of FIG. 7 toFIG. 9 may also be easily extended to a carrier aggregation (orbandwidth aggregation) condition by replacing the subframe with acomponent carrier.

Referring to FIG. 10, if the number of frequency bands used for downlinkis greater than the number of frequency bands used for uplink, ACK/NACKinformation for multiple downlink PDSCH transmission should betransmitted through an uplink PUCCH, wherein the number of frequencybands is smaller. For example, the PUCCH for downlink component carriersD and E (D_(DL) and E_(DL)) should be transmitted only through at leastone of uplink component carriers A, B, and C (A_(UL), B_(UL), andC_(UL)). However, the uplink component carriers A, B, and C (A_(UL),B_(UL), and C_(UL)) may essentially be set to respectively transmit thePUCCH for the downlink component carriers A, B, and C (A_(DL), B_(DL),and C_(DL)). Therefore, at least one of the uplink component carriers A,B, and C (A_(UL), B_(UL), and C_(UL)) should further transmit the PUCCHfor downlink component carriers D and E (D_(DL) and E_(DL)).

Accordingly, as shown in FIG. 7 to FIG. 9, the downlink componentcarriers A, B, and C (A_(DL), B_(DL), and C_(DL)) may be referred to aspaired component carriers, and the downlink component carriers D and E(D_(DL) and E_(DL)) may be referred to as non-paired component carriers.However, in a carrier aggregation (or bandwidth aggregation) condition,the PDCCH and the PDSCH linked to the PDCCH may each be transmittedthrough a different DL CC. Therefore, the paired state may be definedbased upon the DL CC through which the PDCCH is transmitted. Conversely,the paired state may also be defined based upon the DL CC through whichthe PDSCH is transmitted. Multiple data units may be simultaneously(e.g., during the same subframe) received in the FDD mode, and themultiple data units may also be respectively received at the same pointor at different points through multiple subframes in the TDD mode.

Hereinafter, with reference to FIG. 11 to FIG. 15, diverse exemplarymethods of transmitting ACK/NACK signals for multiple PDSCHs withinmultiple downlink subframes (or DL CCs) through a single uplink subframe(or UL CC) will be described. For simplicity of the description, amethod for transmitting ACK/NACK signals for the PDSCHs within twodownlink subframes (or DL CCs) through a single uplink subframe (or ULCC) will be given as an example.

For simplicity of the description, the description will be mostlyfocused on the case wherein multiple data units are being receivedthrough a paired DL subframe (or DL CC) and/or a non-paired DL subframe(or DL CC). However, this is merely exemplary, and, therefore, thedescription may similarly apply to a case wherein the user equipmenttransmits data units, which are received through at least three or moreDL subframes (or DL CCs), through a single UL subframe (or UL CC).

Embodiment 1 Reservation of Additional Resource

FIG. 11 illustrates an example of assigning (or allocating) resourcesfor transmitting ACK/NACK signals according to an embodiment of thepresent invention. This embodiment of the present invention shows anexample of a case wherein additional resource is reserved in the PUCCHresource region so as to be assigned to the PUCCH for ACK/NACKtransmission. More specifically, when the user equipment receivesmultiple PDCCHs and the respective PDSCH, a PUCCH index may be decidedfrom the already-reserved resource in accordance with the receivedsubframe (or DL CC) through which the PDCCH (or PDSCH) is received. Theadditionally reserved PUCCH resource may be set so that the additionallyreserved PUCCH resource does not overlap with the already-existingreserved PUCCH resource, or may be set so that the additionally reservedPUCCH resource can partially overlap with the already-existing reservedPUCCH resource. The additional resource may be explicitly indicatedthrough an RRC message or L1/L2 control information, or the additionalresource may be implicitly signaled from example from the type, index,and so on of the subframe (or DL CC). Although the additional resourcewill not be limited only to the above-described example, the additionalresource may be reserved by applying an offset in Equation 1.

Referring to FIG. 11, the user equipment may decide the PUCCH index forthe PDSCH received through the paired subframe (or DL subframe 1) bydirectly using a specific (e.g., first) CCE index used for PDCCHtransmission. Meanwhile, the user equipment may decide the PUCCH indexfor the PDSCH received through the non-paired subframe (or DL subframe0) from the additional resource by applying an offset to the specific(e.g., first) CCE index used for PDCCH transmission. This embodiment ofthe present invention may also be applied by setting a different valuefor the N⁽¹⁾ _(PUCCH) in Equation 1, instead of applying an offset tothe CCE index.

Embodiment 2 Null PDCCH Transmission

FIG. 12 illustrates an example of deciding PUCCH resources fortransmitting ACK/NACK signals according to another embodiment of thepresent invention. In this embodiment of the present invention, anexample of transmitting a null PDCCH for a PUCCH assignment (orallocation) used for ACK/NACK transmission is given. Basically, in a ULsubframe, a PUCCH resource is linked to a CCE index of a PDCCH beingtransmitted from a paired DL subframe. Therefore, when the userequipment receives a PDCCH through a non-paired DL subframe, a PDCCH forassigning PUCCH resources may be separately defined. Herein, the PDCCHis transmitted through a paired DL subframe for PUCCH resourceassignment (or allocation). For simplicity, the PDCCH for assigningPUCCH resources will be referred to as a null PDCCH. More specifically,the null PDCCH corresponds to a PDCCH being transmitted through a pairedDL subframe for a non-paired DL subframe, and the null PDCCH provides aCCE index for PUCCH resource assignment (or allocation). The null PDCCHmay be identified by using contents of control information (e.g., null(e.g., predefined ‘0’s or ‘1’s) value, pre-decided specific value,etc.), a structure of the control information (e.g., DCI format, length,etc.), an RNTI (Radio Network Temporary Identity) for CRC (CyclicRedundancy Check) masking, a code for scrambling, and so on. The nullPDCCH may be configured of a small number of CCEs, and,characteristically, the null PDCCH may be configured of 1 CCE. When theuser equipment receives a plurality of non-paired subframes, a pluralityof null PDCCHs may have to be received accordingly. In this case, eachnull PDCCH should be connected to the respective non-paired subframe.For this, the null PDCCH may include non-paired subframe identificationinformation. The non-paired subframe identification information may bedirectly included in control information (e.g., DCI) of the null PDCCH,or may be indirectly indicated by using a masking/scrambling code. Also,each null PDCCH may be automatically linked to a respective non-pairedsubframe taking into consideration of the null PDCCH order (e.g., numberof CCEs, position of a specific (e.g., first) CCE within the frequency).Moreover, when a user equipment receives a plurality of non-pairedsubframes, PUCCH resources allocated to the user equipment may beindicated by each CCE index in a single null PDCCH consisting of aplurality CCEs. Moreover, when a user equipment receives a plurality ofnon-paired subframes, PUCCH resources may be allocated by using PUCCHresource allocation information in one null PDCCH.

Referring to FIG. 12, UE A receives a PDSCH (and a PDCCH delivering (orcarrying) scheduling information on the PDSCH) in a non-paired DLsubframe (DL subframe 0). In this case, the base station transmits anull PDCCH to UE A through a paired DL subframe (DL subframe 1). Afterreceiving the null PDCCH, the user equipment identifies a PUCCH resourcefor ACK/NACK transmission by considering the null PDCCH, preferably byconsidering a resource index related to the null PDCCH. For example, inthis case, the user equipment may use a PUCCH index, which is linked toa specific (e.g., first) CCE of the null PDCCH, so as to transmit theACK/NACK signal for the PDSCH to the base station, wherein the PDSCH isreceived in DL subframe 0. Meanwhile, UE B receives a PDCCH and itsrespective PDSCH through DL subframe 1 and transmits an ACK/NACK signalto the base station through a PUCCH resource, which is linked to aspecific (e.g., first) CCE of the PDCCH.

Embodiment 3 Signaling Additional Information

FIG. 13 and FIG. 14 respective illustrate examples of deciding resourcesfor transmitting ACK/NACK signals according to yet another embodiment ofthe present invention. In this embodiment of the present invention, anexample of signaling additional information for assigning (orallocating) a PUCCH index is given. Regardless of the subframe type, itis assumed in this embodiment of the present invention that the PUCCH islinked with a specific (e.g., first) CCE of corresponding all PDCCHsregardless of subframe type. In this case, when multiple subframes arereceived through multiple PDCCHs, specific (e.g., first) CCE indexes ofthe PDCCH may overlap. Therefore, in order to prevent collision betweenPUCCH resources due to the overlapping CCEs, additional information forchanging the mapping between the CCE index and the PUCCH index may besignaled. In this embodiment of the present invention, the additionalinformation will be simply referred to as index modificationinformation. For example, the index modification information may be anabsolute or relative offset for the PUCCH index. In this case, theoffset may be applied by being added in Equation 1. The indexmodification information may be signaled through the PDCCH. In thiscase, the index modification information may be transmitted through thePDCCH of a paired subframe, or may be transmitted through the PDCCH of anon-paired subframe. Also, regardless of the subframe, the indexmodification information may be transmitted through the PDCCH of bothnon-pd/non-paired subframes. The index modification information may beexplicitly or implicitly signaled. For example, the index modificationinformation may be directly included in the control information of thePDCCH, or may be indirectly indicated by using a masking/scramblingcode. Furthermore, the PDCCH indicates only an on/off state on whetheror not the index should be modified, and the index modifying informationmay be pre-defined or indirectly identified by taking into account ofsubframe type/index, duplex mode, CC index, and so on. For example, whena PDCCH is received through a non-paired subframe, an index of thenon-paired subframe or a value associated therewith may be used as theindex modification information (e.g., offset). For another example, whena PDCCH is received through a non-paired subframe, an index difTerencebetween the non-paired subframe and the paired subframe or a valueassociated therewith may be used as the index modification information(e.g., offset). If the PDCCH is received through a non-paired CC, theindex modification information may be identified in a similar manner.

FIG. 13 assumes a case wherein the index modification information issignaled through the PDCCH of a paired subframe. Referring to FIG. 13,in order to avoid PUCCH collision between UE A and UE B, additionalinformation is signaled to UE B. When it is assumed that an index offsetis signaled to UE B from the base station, UE B adds the received offsetvalue to the PUCCH index, which is linked to the specific (e.g., first)CCE of the PDCCH received in DL subframe 1, thereby deciding the finalPUCCH index. Meanwhile, UE A uses the PUCCH index, which is linked tothe specific (e.g., first) CCE of the PDCCH received in DL subframe 0,so as to transmit an ACK/NACK signal. Therefore, even if the first CCEindex of the PDCCH for UE A is identical to the first CCE index of thePDCCH for UE B, PUCCH collision may be prevented.

FIG. 14 assumes a case wherein the index modification information issignaled through the PDCCH of a non-paired subframe, Referring to FIG.14, in order to avoid PUCCH collision between UE A and UE B, additionalinformation is signaled to UE A. When it is assumed that an index offsetis signaled to UE A from the base station, UE B adds the received offsetvalue to the PUCCH index, which is linked to the specific (e.g., first)CCE of the PDCCH received in DL subframe 0, thereby deciding the finalPUCCH index. Meanwhile, UE B uses the PUCCH index, which is linked tothe specific (e.g., first) CCE of the PDCCH received in DL subframe 1,so as to transmit an ACK/NACK signal. Therefore, even if the first CCEindex of the PDCCH for UE A is identical to the first CCE index of thePDCCH for UE B, PUCCH collision may be prevented.

Embodiment 4 Indexing Based Upon a CCE Subsequent to the First CCE

FIG. 15 illustrates an example of deciding resources for transmittingACK/NACK signals according to yet another embodiment of the presentinvention. In this embodiment of the present invention, an example ofdeciding a PUCCH index based upon a CCE index subsequent to the firstCCE of the PDCCH for PDSCH-scheduling is given. In the LTE system, whentwo or more CCEs are used for PDCCH transmission, the PUCCH indexesmapped to the remaining CCEs excluding the first CCE are not used forPUCCH transmission. More specifically, the base station reserves anumber of PUCCH resources corresponding to the number of CCEs used forPDCCH transmission. Therefore, when the user equipment decides PUCCHresources based upon the CCE index subsequent to the first CCE index,collision between the ACK/NACK signals may be prevented.

Referring to FIG. 15, the PUCCH index for a paired DL subframe (DLsubframe 1) is decided by the first CCE index used in the correspondingPDCCH transmission. Conversely, the PUCCH index for a non-paired DLsubframe (DL subframe 0) is decided by a CCE subsequent to the first CCEindex used in the corresponding PDCCH transmission, preferably PDCCHtransmission of the paired DL subframe. Therefore, additional signalingis not required for resource assignment (or allocation). Meanwhile, whentwo or more CCEs are consecutively assigned for the PDSCH transmission,the index subsequent to the first CCE index will become the second indexfor the PDCCH transmission. In this case, since multiple PUCCH indexeshave already been exclusively reserved based upon the CCEs assigned forthe PDCCH transmission, collision between identical/different userequipments may be automatically prevented. Meanwhile, when the PDCCH,which is transmitted through a (non-)paired subframe, is configured of asingle CCE, a collision may occur between the PUCCH indexes ofidentical/different user equipments. If a single CCE is assigned forPDCCH transmission of UE A, in order to prevent collision with otheruser equipment, the base station should perform scheduling so that aPDCCH (particularly the first CCE of the PDCCH) of another userequipment would not be transmitted using a CCE subsequent to the firstCCE for the PDCCH of UE A.

In this embodiment of the present invention, when the user equipmentrequires N(>2) PUCCH resources, expansion may be simply performedwithout any additional signaling. More specifically, additional (N−1)PUCCH indexes may be consecutively assigned in accordance with a seriesof consecutive (N−1) CCE indexes subsequent to the first CCE index.

As shown in FIG. 11 to FIG. 15, UE A and UE B may correspond to the sameuser equipment or may each correspond to a different user equipment. IfUE A and UE B correspond to the same user equipment, the user equipmenttransmits ACK/NACK signals for multiple data units, which are receivedthrough multiple downlink subframes (or DL CCs), to the base station (orrelay station) through linked PUCCH resources. In this case, the userequipment may individually transmit an ACK/NACK signal for each of themultiple data units through a respective PUCCH resource. Furthermore,instead of using all of the multiple PUCCH resources, a bundled ormultiplexed ACK/NACK signal may be transmitted through one or moreselected PUCCH resources.

In the embodiment of the present invention, at least part of theembodiment may be easily applied for a different purpose (e.g.,additional PUCCH assignment for transmission diversity). For example,the paired subframe shown in the example according to the embodiment ofthe present invention may be re-interpreted as one of multipletransmission antennae. And, the non-paired subframe may bere-interpreted as the remaining transmission antennae. In this case, inorder to ensure additional PUCCH resources for the remainingtransmission antennae, the PUCCH index may be changed by using a similarmethod as shown in the example according to the embodiment of thepresent invention.

FIG. 16 is a diagram illustrating a base station and a user equipmentthat can be applied to one embodiment of the present invention.

Referring to FIG. 16, the wireless communication system includes a basestation (BS) 110 and a user equipment (UE) 120. In the downlink, thetransmitter is a part of the base station 110 and the receiver is a partof the user equipment 120. In the uplink, the transmitter is a part ofthe user equipment 120 and the receiver is a part of the base station110. The base station 110 includes a processor 112, a memory 114, and aradio frequency (RF) unit 116. The processor 112 can be configured toimplement procedures and/or methods suggested in the present invention.The memory 114 is connected with the processor 112 and stores variouskinds of information related to the operation of the processor 112. TheRF unit 116 is connected with the processor 112 and transmits and/orreceives a radio signal. The user equipment 120 includes a processor122, a memory 124, and a radio frequency (RF) unit 126. The processor122 can be configured to implement procedures and/or methods suggestedin the present invention. The memory 124 is connected with the processor122 and stores various kinds of information related to the operation ofthe processor 122. The RF unit 126 is connected with the processor 122and transmits and/or receives a radio signal. The base station 110and/or the user equipment 120 can have a single antenna or multipleantennas.

The aforementioned embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment. Moreover, it will be apparent that someclaims referring to specific claims may be combined with another claimsreferring to the other claims other than the specific claims toconstitute the embodiment or add new claims by means of amendment afterthe application is filed.

The embodiments of the present invention have been described based onthe data transmission and reception between the base station and theuser equipment. A specific operation which has been described as beingperformed by the base station may be performed by an upper node of thebase station as the case may be. In other words, it will be apparentthat various operations performed for communication with the userequipment in the network which includes a plurality of network nodesalong with the base station can be performed by the base station ornetwork nodes other than the base station. The base station may bereplaced with terms such as a fixed station, Node B, eNode B (eNB), andaccess point. Also, the user equipment may be replaced with terms suchas mobile station (MS) and mobile subscriber station (MSS).

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, or theircombination. If the embodiment according to the present invention isimplemented by hardware, the embodiment of the present invention can beimplemented by one or more application specific integrated circuits(ASICs), digital signal processors (DSPs), digital signal processingdevices (DSPDs), programmable logic devices (PLDs), field programmablegate arrays (FPGAs), processors, controllers, microcontrollers,microprocessors, etc.

If the embodiment according to the present invention is implemented byfirmware or software, the embodiment of the present invention may beimplemented by a type of a module, a procedure, or a function, whichperforms functions or operations described as above. A software code maybe stored in a memory unit and then may be driven by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various means whichare well known.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

The present invention may be applied in a wireless communication system.More specifically, the present invention may be applied to a method andapparatus of transmitting ACK/NACK.

What is claimed is:
 1. A method for transmitting an uplink signal by auser equipment (UE) in a wireless communication system, the methodcomprising: receiving, by the UE, a physical downlink control channel(PDCCH) via one or more resource units; receiving, by the UE, a physicaldownlink shared channel (PDSCH) indicated by the received PDCCH; andtransmitting, by the UE, a physical uplink control channel (PUCCH) usinga PUCCH resource in response to the received PDSCH, wherein an index ofthe PUCCH: resource is determined by adding a first index offset and asecond index offset to a lowest index of the one or more resource units,and wherein the first index offset is signaled via the PDCCH and thesecond index offset is signaled via higher layer signaling.
 2. Themethod of claim 1, wherein the PDSCH carries a downlink data signal andthe PUCCH carries an acknowledgement/negative-acknowledgement (ACK/NACK)signal for the downlink data signal.
 3. The method of claim 1, whereinthe first index offset is signaled through downlink control information(DCI) which is carried by the PDCCH.
 4. The method of claim 1, whereineach of the one or more resource units corresponds to a control channelelement (CCE).
 5. The method of claim 4, wherein the lowest indexcorresponds to a lowest CCE index used to construct the PDCCH.
 6. Themethod of claim 1, wherein the second index offset is signaled throughan RRC message.
 7. A user equipment (UE) configured to transmit anuplink signal in a wireless communication system, the UE comprising: aradio frequency (RF) unit; and a processor configured to: receive aphysical downlink control channel (PDCCH) via one or more resourceunits, receive a physical downlink shared channel (PDSCH) indicated bythe received PDCCH, and transmit a physical uplink control channel(PUCCH) using a PUCCH resource in response to the received PDSCH,wherein an index of the PUCCH resource is determined by adding a firstindex offset and a second index offset to a lowest index of the one ormore resource units, and wherein the first index offset is signaled viathe PDCCH and the second index offset is signaled via higher layersignaling.
 8. The UE of claim 7, wherein the PDSCH carries a downlinkdata signal and the PUCCH carries anacknowledgement/negative-acknowledgement (ACK/NACK) signal for thedownlink data signal.
 9. The UE of claim 7, wherein the first indexoffset is signaled through downlink control information (DCI) which iscarried by the PDCCH.
 10. The UE of claim 7, wherein each of the one ormore resource units corresponds to a control channel element (CCE). 11.The UE of claim 10, wherein the lowest index corresponds to a lowest CCEindex used to construct the PDCCH.
 12. The UE of claim 7, wherein thesecond index offset is signaled through an RRC message.